lny=xln(1+sinx)
y'/y=ln(1+sinx)+xcosx/(1+sinx)
y'=(1+sinx)^x [ln(1+sinx)+xcosx/(1+sinx)]
dy=(1+sinx)^x [ln(1+sinx)+xcosx/(1+sinx)]dx
dy|x=π/2
=2^(π/2)【ln2+0】
ln2* 2^(π/2)